Written by Beata Anderson, Advanced Practitioner Sonographer
As a sonographer we get asked very often if a baby can hear or when do they develop hearing while growing inside the uterus.
The early formation of what will become your baby’s eyes and ears begins in the second month of your pregnancy. That’s when the cells inside the developing baby begin arranging themselves into what will become the face, brain, nose, eyes, and ears. At roughly 9 weeks, little indentations in the side of your baby’s neck appear as the ears continue to form on both the inside and the outside. Eventually, these indentations will begin moving upward before developing into what you’ll recognize as your baby’s ears.
Around 15 weeks your baby will start to hear. They may hear muted sounds from the outside world and any noises your digestive system makes, as well as the sound of your voice and heart. The eyes also start to become sensitive to light. Even though your baby’s eyes are closed, they may register a bright light outside your tummy.
Around 18 weeks of pregnancy, your little one hears their very clear first sounds. By 24 weeks, those little ears are rapidly developing. Your baby’s sensitivity to sound will improve even more as the weeks pass. The limited sounds your baby hears around this point in your pregnancy are noises you may not even notice. They are the sounds of your body. These include your beating heart, air moving in and out of your lungs, your growling stomach, and even the sound of blood moving through the umbilical cord.
As your baby grows, more sounds will become audible to them. Around week 25 or 26, babies in the womb have been shown to respond to voices and noise. Recordings taken in the uterus reveal that noises from outside of the womb are muted by about half. That’s because there’s no open air in the uterus. Your baby is surrounded by amniotic fluid and wrapped in the layers of your body. That means all noises from outside your body will be muffled. The most significant sound your baby hears in the womb is your voice. In the third trimester, your baby can already recognise it. Research has shown that a baby’s heart rate increases after hearing its mother’s voice, meaning your baby is more alert when you’re speaking (Fruhholz S, Belin P. The Oxford Handbook of Voice Perception. Oxford University Press, 2018).
As a result, it is a great idea to talk to your growing baby. You also can read books and sing lullabies. In fact, research indicates that babies hear what their mothers say and recognise these words after birth. Interestingly, the study also found that babies can detect subtle changes and process complex information. During the study, researchers at the University of Helsinki in Finland, looked at 33 expectant mothers and examined their babies after birth. While pregnant, 17 of the mothers listened to a CD at a high volume with made-up words said in different ways and with different pitches from week 29 to birth. Overall, the mothers and their babies heard the nonsense words about 50 to 71 times. (Partanen E, Kujala T, Näätänen R, Liitola A, Sambeth A, Huotilainen M. Learning-induced neural plasticity of speech processing before birth. Proc Natl Acad Sci USA. 2013;(110)37:15145-50. doi:10.1073/pnas.1302159110). Then, following their births, the researchers tested all 33 babies for normal hearing, and then performed an EEG brain scan to see how the new-borns responded to the made-up words. For the babies that heard the nonsense words while in utero, their brain activity picked up when those words were played. The babies who did not hear the words did not react much. The researchers concluded that an unborn baby can learn and remember just as well as a new-born. Consequently, they believe it may be worthwhile to expose babies to more sounds before they are born.
Reading books and singing lullabies – all of these things not only allow you and your partner to stimulate and support your growing baby’s hearing, but also allow you both to bond with your unborn baby.
I hope you found this blog useful. We may ask you to talk to your baby to encourage your baby to respond during your scan to help us get all the pictures and views we need to complete our checks.